Frequency‐dependent characteristics of nerve‐mediated ATP and acetylcholine release from detrusor smooth muscle

Abstract

Nerve-mediated contractions of detrusor smooth muscle are mediated by acetylcholine (ACh) and ATP release in most animals. However, with the normal human bladder, only ACh is a functional transmitter, but in benign pathologies such as overactive bladder (OAB), ATP re-emerges as a secondary transmitter. The selective regulation of ATP release offers a therapeutic approach to manage OAB, in contrast to current primary strategies that target ACh actions. However, the release characteristics of nerve-mediated ACh and ATP are poorly defined and this study aimed to measure the frequency dependence of ACh and ATP release and determine if selective regulation of ATP or ACh was possible. Experiments were carried out in vitro with mouse detrusor with nerve-mediated ATP and ACh release measured simultaneously with tension recording. ATP was released in two frequency-dependent components, both at lower frequencies (mid-range 0.4 and 5.5 Hz stimulation) compared to a single compartment release of ACh at 14 Hz. Intervention with the phosphodiesterase type-5 inhibitor sildenafil attenuated ATP release, equally from both components, but had no effect on ACh release. These data demonstrate that nerve-mediated ACh and ATP release characteristics are distinct and may be separately manipulated. This offers a potential targeted drug model to manage benign lower urinary tract conditions such as OAB.

Selective reduction of neurotransmitter release by cAMP-dependent pathways in mouse detrusor

“…It is unclear if differential neurotransmitter release is from different populations of nerves, or from different vesicles in the same varicosities. This study suggests that ATP and ACh can be separately released from motor efferent nerves that innervate bladder detrusor smooth muscle, and this is consistent with their different frequency dependencies ( 28 ) and the ability to manipulate differential release by modulation of cyclic nucleotides by PDE 5 inhibitors like sildenafil ( 27 , 28 ), or adenosine A 1 receptor activation. It has been demonstrated in several studies that adenosine A 1 receptor activation can modulate neurotransmitter release ( 50 ), suggesting a potential role for the modulation of cyclic nucleotides and downstream effects on protein kinases in the selective inhibition of purinergic neurotransmissions.…”

“…1, C and D ) were fitted to a linear two-component function, Eq. 1b , as this yielded a significantly better fit than a one-component function ( 28 ): Y ( f ) is equivalent to either T ( f ) or [ATP]( f ). …”

“…Young (12 wk) male C57BL/6 mice (Harlan UK, Ltd.) were used for experiments. The animal model was chosen to conform with previous experiments where transmitter release methods were validated ( 27 , 28 ) and according to the stipulations of the funding authority (NIH).…”

“…Frequency-dependent ACh data were fitted to a one-component function, Eq. 1c ; there was no statistical advantage by fitting ACh data to a two-component model ( 28 ). …”

Purine and purinergic receptors in health and disease

“…Deficiency in P2X1R may lead to inflammation‐induced damage to intestinal vascular integrity and severe hemorrhaging 53 . Additionally, P2X1R is also implicated in bladder dysfunction 54 . P2X2R and P2X3R play a role in regulating somatic sensation, and their antagonists have the potential to abolish responses to taste stimuli 55 .…”